Heretofore, a transparent conductive film has been suitably used as a transparent electrode or electromagnetic shielding material for a liquid crystal display, transparent touch panel or the like. As the transparent conductive film, a film formed by coating at least one surface of a transparent film such as polyethylene terephthalate (PET) or triacetyl cellulose (TAC) with indium oxide (In2O3), tin oxide (SnO2), a sintered mixture (ITO) of In2O3 and SnO2 by a dry process such as vacuum deposition, sputtering or ion plating is known.
However, when the transparent conductive film is used as a transparent electrode or electromagnetic shielding material, it is generally subjected to continuous processing or punching in the form of a web or used or stored in a bent state during a surface treatment. Thus, the above transparent conductive film obtained by the dry process cracks during the above processing or storage, resulting in an increase in surface resistance.
Further, when a metal oxide such as ITO is used as a transparent conductive material, for example, the refractive index of ITO is so high as about 1.8 that surface reflectivity becomes high, whereby sufficient transmittance cannot be obtained. Accordingly, there has been proposed a method of obtaining a conductive film having high transmittance by forming a low refractive layer such as silica, and a high refractive layer such as titanium oxide as required, between an ITO layer and a base material film so as to develop an antireflective effect (refer to Japanese Patent Laid-Open Publication No. 207128/2000).
Meanwhile, in a transparent conductive coating layer formed by coating a transparent base material film with a conductive polymer (wet process), the coating layer is flexible and hardly has a problem such as cracking. Further, the process of obtaining the transparent conductive film by applying a conductive polymer has advantages that its production cost is relatively low as compared with a dry process and that it is highly productive since coating speed is generally high. Polythiophene, polyaniline, polypyrrole and the like which have been generally used in such a transparent conductive film obtained by application of a conductive polymer have problems that their use is limited to an antistatic application and the like because high conductivity cannot be obtained in the initial stage of development and that the hue of the conductive coating layer itself is unsatisfactory. However, these problems have been recently improved by improvements of production processes. For example, a conductive polymer (refer to Japanese Patent Laid-Open Publication No. 1-313521) comprising polyanions and poly(3,4-dialkoxythiophene) obtained by oxidative-polymerizing 3,4-dialkoxythiophene in the presence of polyanions shows very low surface resistance while keeping high light transmittance due to improvements of production processes in recent years (refer to Japanese Patent Laid-Open Publications Nos. 193972/2002 and 286336/2003).
However, when conductive films using these conductive polymers as a transparent conductive coating layer are applied to various applications, there is a problem of performance degradation caused by separation between the transparent conductive coating layer and the base material film by application of an external force. A representative example of applying the conductive film using the conductive polymer to an application in which an external force is aggressively applied to the film is a touch panel. Although it is proposed in Japanese Patent Laid-Open Publication No. 109998/2002, the above problem is not mentioned.
Further, because the transparent conductive coating layer of the conductive films using these conductive polymers as the transparent conductive coating layer has a low refractive index of around 1.5, it is difficult to improve antireflectivity and light transmittance by placing a layer having a lower refractive index between the conductive coating layer and the base material film. Further, no highly productive process has been found even in a case where an antireflective effect is developed by a combination of the conductive coating layer with a material having a high refractive index. It is the current situation that no conductive film which has sufficiently controlled surface reflectivity and is also highly useful has been proposed.